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It is sometimes suggested that space ports, or at least launch pads, should be constructed on the Moon to support water exports and on Mars to support large scale exploration and settlement. I get the impression that what is proposed is to have a rover flatten the surface, maybe using additive manufacturing or sintering of the regolith. Space ports on Earth are not constructed that easily. SpaceX's new Texan space port requires a pretty huge operation. 300,000 cubic feet of soil will be moved, twice. The alternative would be to put many steel reinforced concrete pillars 200 feet deep.

Is it that much harder to build a space port on Earth because of the active erosion here? Or are space ports in space futuristic mega projects which cannot even begin until Mars has already been settled by humans?

http://www.parabolicarc.com/2016/04/18/giant-pile-dirt-marks-spacexs-texas-launch-site/

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    $\begingroup$ I feel that constructing the spaceport would be the easier half. The more difficult half is building the rockets (or at least the rocket fuel manufacturing facilities) on the Moon or Mars. $\endgroup$
    – Lightsider
    Commented Apr 20, 2016 at 13:14
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    $\begingroup$ One thing that immediately comes to mind is that a space port on the Moon would not have to handle as heavy loads. I'm not sure how much easier that will make the construction process. $\endgroup$
    – called2voyage ♦
    Commented Apr 20, 2016 at 13:15

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You need a flat surface, that is it.

The Apollo lunar landers landed at the Moon, without any present infrastructure. The descent stage then served as a space port pocket edition.

As a zero-infrastructure solution is possible, improving on that is trivial. Any action that makes the landing zone flatter or larger, and removes disturbing rocks and cliffs is helping, improving the site's quality as a space port. Additionally, a few pieces of navigation helping equipment can be deployed to make operations more accurate.

This may sound like a cheap argument, and it is. But the actual difficult and labour requiring infrastructure is not really directly tied to the space port itself. It is the production of space craft, components, materials and fuel in-situ that is the difficult part. The space port itself can be as simple as you desire.

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One big factor is Earth's gravity.

To reach space from Earth, any spacecraft needs to be huge. It requires a huge crawler and good crawlerway. It requires a solid, big launchpad to support the weight of the craft and infrastructure to keep it upright, fueling it with hundreds or thousands of tons of fuel, keeping it powered, and safe against the environment (including undisciplined bystanders). The mighty engines require flame trenches to contain the blast of the exhaust and protect the craft from it. There's a big water tower and a massive sprinkling (more like flooding) system to extinguish the sound waves from the launch which are enough to destroy the craft.

This all weighs a lot and needs structural infrastructure to support it and keep it from simply sinking into the soil or breaking under own weight. That's why Earth spaceports are so huge.

On the Moon, the delta-V needed to reach Moon orbit is way, way smaller, and taking the Rocket Equation into account, the needed size of the craft is exponentially smaller. Smaller engines, as not nearly as much thrust is needed. Way smaller tanks. Supply pipes and cables that will not snap under own weight. That means far less - exponentially less - infrastructure needed to support the launch. Your craft will be maybe 20 ton instead of 20,000, for similar payload to the orbit. Even completely independently of the same structural construction being able to support six times the mass it could support on Earth, simply due to everything being lighter!

Mars lies somewhere in the middle mass-wise, but again, the rocket equation with its exponent is on our side, reducing the mass exponentially in relation to the gravity. You might need more infrastucture, but really, a simple slab of concrete (or something similar) will suffice where the launchpad with flame trenches and water dump system was required.

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  • $\begingroup$ So, not even a flame trench is needed on Mars or the Moon? Is so little thrust neede that the flames won't damage the pad or bounce back to damage the launcher? The Apollo landing stage was indeed sufficient as launch pad. The Grasshoper test rocket of SpaceX is maybe an example of using a simple launch pad for a low thrust take off. $\endgroup$
    – LocalFluff
    Commented Apr 21, 2016 at 11:13
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    $\begingroup$ @LocalFluff: With near-vacuum, the flames dissipate much more readily. Probably there would be some deflector directing the flames to the sides, maybe even some channels to keep them away, and of course lower thrust, but definitely no heavyweight trench - for basic launch vehicles. If one tries to launch something the size of Space Shuttle (launch mass) from Mars, the case would be different. Also, with Martian gravity, the initial TWR can be lower, so the rocket can launch throttled and reach full power some way above the ground. $\endgroup$
    – SF.
    Commented Apr 21, 2016 at 11:28
  • $\begingroup$ ...also, the same thrust that carries the Grasshopper, could carry a vessel three times as massive, and have respectively more delta-V, vs the reduced delta-V requirements of the planet. Also compare to START, TOPOL and other mobile ICBMs. They can be deployed in rough terrain within 20 minutes and have enough delta-V to reach escape velocity from Mars. $\endgroup$
    – SF.
    Commented Apr 21, 2016 at 16:05
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The spaceport SpaceX is building in Texas consists of at least the following:

  • launch pad capable of supporting the Falcon Heavy, FH weight is in the region of 1500 tons.
  • a building for horizontal assembly of the FH, i.e. 75+ m long, and capable of supporting 30-ton capacity gantry cranes that have to be in precise positions to assemble the rocket.

Both of these require good foundations, because the terrain consists of soil: loose, compressible material.

For now, all we need on Mars is a launch pad that can support an ascent stage that can reach Mars orbit, and that can weigh as little as 22 tons. Maybe a bit more to accommodate the larger lander that brings the ascent stage down. Clearing away the loose regolith until you encounter solid rock would be an easy way to construct such a launch pad. Add a few blast barriers and you're done.
It's not until you start building rockets on Mars that you need a Texas-scale spaceport.

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  • $\begingroup$ Refueling is envisioned for takeoffs from both Mars and the Moon. But I suppose that mass and stable foundations are not the challenges with that. $\endgroup$
    – LocalFluff
    Commented Apr 21, 2016 at 11:16

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